th the zone identifier.


    **Examples:**

    Using the US Eastern time zone as an example, we can see that a ``tzfile``
    provides time zone information for the standard Daylight Saving offsets:

    .. testsetup:: tzfile

        from dateutil.tz import gettz
        from datetime import datetime

    .. doctest:: tzfile

        >>> NYC = gettz('America/New_York')
        >>> NYC
        tzfile('/usr/share/zoneinfo/America/New_York')

        >>> print(datetime(2016, 1, 3, tzinfo=NYC))     # EST
        2016-01-03 00:00:00-05:00

        >>> print(datetime(2016, 7, 7, tzinfo=NYC))     # EDT
        2016-07-07 00:00:00-04:00


    The ``tzfile`` structure contains a fully history of the time zone,
    so historical dates will also have the right offsets. For example, before
    the adoption of the UTC standards, New York used local solar  mean time:

    .. doctest:: tzfile

       >>> print(datetime(1901, 4, 12, tzinfo=NYC))    # LMT
       1901-04-12 00:00:00-04:56

    And during World War II, New York was on "Eastern War Time", which was a
    state of permanent daylight saving time:

    .. doctest:: tzfile

        >>> print(datetime(1944, 2, 7, tzinfo=NYC))    # EWT
        1944-02-07 00:00:00-04:00

    Nc